Supercritical fluids are finding wide acceptance in a number of analytical disciplines as unique solvation media. By far, the largest number of applications occur in the field of chromatography, where these dense gases are employed as extraction solvents and interactive mobile phases.
Historically, supercritical fluid chromatography has its origins in the mid-1960s, while its extraction analogue has only recently seen application in the field of analytical chemistry.
Supercritical fluid extraction is a technique whereby organic compounds can be extracted from sample matrices utilizing a dense carbon dioxide gas. The solvation power of carbon dioxide is increased as the pressure and temperature are increased above their critical points which are 1070 psi and 31.degree. C. respectively.
U.S. Pat. Nos. 4,816,159 and 4,880,543 to Khosah et al disclose supercritical fluid chromatography methods which utilize specific packing materials. The packing materials disclosed in these patents are selected from metal oxide/hydroxide support materials having phosphorous-containing organic molecules bonded to reactive sites on the support materials.
U.S. Pat. Nos. 4,547,292 to Zarchy; 4,770,780 to Moses; 4,824,570 to Bethuel et al; 4,877,530 to Moses; and International Patent No. WO 85/04816 each disclose various processes or systems useful for practicing extraction utilizing supercritical fluids.
U.S. Pat. No. 4,898,673 to Rice et al discloses a dynamic supercritical fluid extraction system wherein solid samples are circulated in a mixture of carbon dioxide. This patent notes that liquid samples may be extracted in the dynamic system by absorbing the liquid samples on a solid carrier such as diatomaceous earth.
A number of articles authored or coauthored by one of the present inventors which discuss extraction methods that utilize supercritical fluids include the following:
Favati et al, "Supercritical CO.sub.2 Extraction of Carotene and Lutein from Leaf Protein Concentrates", J. Food Science, Vol. 53, No. 5, pp. 1532-1536 (1988).
King, "Fundamentals and Applications of Supercritical Fluid Extraction in Chromatographic Science", J. Chromatographic Science, Vol. 27 pp. 355-364 (1989).
King et al, "Extraction of Fat Tissue from Meat Products with Supercritical Carbon Dioxide", J. Agricultural & Food Chemistry, Vol. 37, No. 4 pp. 951-954 (1989).
In the above, previous work by one of the present inventors it was found that lipids were completely soluble in supercritical carbon dioxide at 5 liter/min., 10,000 psi and 80.degree. C. These conditions allowed a significant amount of lipids to be extracted from fatty foods in a reasonable time.
It was further discovered that water interferes with the supercritical carbon dioxide extraction of lipids from fatty foods. Complete extraction of lipids from moist fatty foods was achieved after drying the fatty foods over night in a forced air oven at 50.degree. C. This technique worked well but was time consuming and had the potential for losing volatile components such as pesticides which may be contained in the lipids.
The present invention is an improvement over previous supercritical fluid extraction methods and provides for enhancement of extraction utilizing supercritical fluids.